Non-contact musical control devices have been known in the past which issue control instructions by optically detecting the movement of a hand or the like within a specified space. These devices provided a pair consisting of one light source (infrared emitting diode or the like) which shines a light into the space and one light receiving element (infrared sensor or the like) which receives the light of the light source which has been reflected by the hand when said hand proceeds into said space, and if reflected light was received by the light receiver, the device performed a switch-like control which turned the instruction for a specified operation ON when said received light quantity exceeded a certain threshold value, and turned it OFF when it was below the threshold value.
The intensity distribution of the light beam irradiated from the light source in the conventional non-contact musical control devices described above is as shown, for example, in FIG. 26. In this case, the light quantity received by the light receiver will differ, even if the hand is held at the same height from the light receiver, when the hand is held directly above the light source as compared to when it is held to the side. Consequently, in a case where ON/OFF operation instructions are performed according to whether or not the quantity of received light exceeds a specified threshold value, the probability of erroneous operation is high if the operation instruction is performed based purely on the height of the hand as the only scale. In other words, a problem with this type of prior musical control device is that it was difficult for the operator to discern at what proximity to the sensor the switch will be turned ON or OFF. In addition, the type of the operation instruction was limited to whether to perform a certain control, i.e., no more than the binary ON/OFF control of a single specified process could be accomplished.